JP4699317B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device mounted on an optical disc apparatus that optically records or reproduces information on an information recording medium such as an optical disc. Specifically, the present invention relates to an optical pickup device capable of performing an accurate recording / reproducing operation with respect to an optical disc having a plurality of recording / reproducing layers.

  In recent years, optical discs are capable of recording a large amount of information signals at high density, and thus are being used in many fields such as audio, video, and computers.

  A compact disk (CD), a video disk, a mini disk (MD), a magneto-optical disk for computers, and the like that are currently commercially available use a substrate having a thickness of 1.2 mm. The objective lens of the optical pickup is also designed to correct aberrations caused by a 1.2 mm thick substrate.

  On the other hand, various studies have been made to increase the recording capacity. Among them, there are a method of increasing the numerical aperture (NA) of the objective lens to improve optical resolution, a method of providing recording layers in multiple layers, and the like.

  For example, Japanese Patent Laid-Open No. 5-151609 discloses an optical disc apparatus for individually reproducing recorded data of each layer from an optical disc having multiple data layers. Here, the recording / reproducing layer of the multi-layer disc is formed by alternately stacking transparent substrates and air layers, and information recording / reproducing is performed on each recording / reproducing layer by focusing an objective lens in the optical axis direction by an actuator. Do.

  In this example, since the distance between each layer is sufficiently large, there is no influence of the return light coming from the adjacent recording / reproducing layer. For example, the focus error signal (FES) in the nth layer is not in the n + 1th or n−1th layer. 0, and no adverse effect such as offset is exerted on the FES of other layers. However, since the distance between each layer is greatly separated, when the focus servo is applied to each layer, the overall thickness of the disk substrate to be adjusted greatly changes. Therefore, it is necessary to separately correct the spherical aberration generated on each surface by the aberration compensator.

  As a solution to the above problem, a two-layer disc in which data layers are stacked with an interlayer distance sufficiently thin with respect to the thickness of the substrate (for example, a distance of about 40 to 70 μm) has been proposed as a digital versatile disc (DVD). ing. In this case, since the spherical aberration generated due to the difference in the substrate thickness is sufficiently small, an aberration compensator is not necessary.

However, in such a disc on which recording / reproducing surfaces are stacked with such a thin interlayer distance, when a light beam accesses one recording / reproducing surface, reflected light from the recording / reproducing surface is adjacent to the recording / reproducing surface. It will be affected by the return light from the playback surface. Therefore, the FES for adjusting the focus of the light beam is also affected by the above effect, and accurate focus adjustment cannot be performed.
Japanese Patent Laid-Open No. 5-151609 (released on June 18, 1993)

  The present applicant has previously proposed an optical system shown in FIGS. 14 and 15 as an optical system for a multi-layered disk formed with a sufficiently thin interlayer distance as described above (application number: Japanese Patent Application No. 7-315642).

  Here, as shown in FIG. 14, the light from the semiconductor laser 1 is condensed on the optical disk 5 by the objective lens 4, and the return light is guided to the light receiving element 6 by the three-part hologram element 2. The semiconductor laser 1, the hologram element 2, and the light receiving element 6 are integrally formed.

  As shown in FIG. 15, the light receiving element 6 has auxiliary light receiving regions 6e and 6f for correcting the focus error signal on both outer sides in addition to the two divided main light receiving regions 6a and 6b for detecting the focus error signal (FES). Have. The main light receiving areas 6a and 6b receive the respective return lights according to the focus direction. The auxiliary light receiving areas 6e and 6f are respectively provided at positions where return light that protrudes from the main light receiving areas 6a and 6b is detected in the defocused state. Then, a focus error signal is detected with a pair of the main light receiving areas 6a and 6b and the auxiliary light receiving areas 6e and 6f that change in the opposite direction to the direction of the shape change of the return light due to the focus.

  Specifically, when the output signals of the light receiving regions 6a, 6b, 6e, and 6f are Sa, Sb, Se, and Sf, the focus error signal FES is calculated by (Sa + Sf) − (Sb + Se). In this way, when the light beam is out of the main light receiving area 6a (or 6b) outside the dynamic range, that is, greatly defocused, the output signal in the auxiliary light receiving area 6e (or 6f) arranged outside the main light receiving area 6a (or 6b). Increases and the focus error signal FES decreases. As a result, the focus error signal FES increases as the distance from the just focus position increases, and becomes a signal that decreases abruptly when the distance exceeds a certain distance. Therefore, if the size and arrangement of the main light receiving areas 6a and 6b and the auxiliary light receiving areas 6e and 6f are appropriately set, only the focus error signal from the recording / reproducing surface during scanning is effective, and the adjacent areas are adjacent. The influence of the return light from the recording / reproducing layer can be eliminated.

  As described above, according to the previously proposed optical pickup device, ideally an accurate focus error signal can be obtained, and a recording / reproducing operation can be performed accurately.

  However, assembling errors naturally exist when assembling the pickup. When such an error occurs, the shape change of the return light to the light receiving element when the focus operation is performed is different, and the correction of the focus error signal is overcorrected, or conversely, the correction is insufficient. When an optical disc having a plurality of recording / reproducing layers is recorded / reproduced, it becomes impossible to obtain a good FES curve.

  Similarly, when an assembly error occurs, the return light to the light receiving area for generating the radial error signal is incident on a position deviated from the ideal position. In addition, it is necessary to increase the area of the light receiving portion so that the light receiving area is within the light receiving region. However, in an optical disk such as a DVD, it is necessary to increase the bandwidth of the light receiving element as the capacity increases, and for this purpose, it is necessary to reduce the area of the light receiving part, which is a condition contrary to the above contents. It becomes.

  The present invention has been made to solve the above-described problems. By optimizing the shape of the auxiliary light receiving area, an optical disc having a plurality of recording / reproducing layers can be obtained even when an assembly error occurs during pickup assembly. On the other hand, an optical pickup device capable of an accurate recording / reproducing operation is provided.

  The optical pickup device of the present invention emits a light beam from a light source, condenses the light beam on the optical recording medium, and detects the return light from the optical recording medium. Focus control means for generating a focus error main signal corresponding to the amount of incident light on each main light receiving area, and at least two main light receiving areas from both sides, having at least two light receiving areas on which return light corresponding to the shift is incident A radial control means that is arranged so as to be sandwiched and has two radial error detection light receiving areas on which return light from the optical recording medium is incident, and detects a radial error signal from the amount of incident light on the radial error detection light receiving area; The radial error detection light-receiving area is formed in a shape inclined with respect to the radial direction of the optical recording medium, and two Area of dialkyl error-detecting light-receiving regions are those substantially identical.

  According to the above configuration, even when there is an arrangement error such as an assembly error, the return light enters the light receiving area for detecting the radial error signal, and the area of the light receiving area can be minimized. This does not hinder the increase in bandwidth of the light receiving element. In addition, since the areas of the left and right light receiving portions are substantially the same, even when stray light from adjacent recording / reproducing surfaces is incident when accessing a recording medium having a plurality of recording / reproducing surfaces, the occurrence of offset can be suppressed. It becomes possible.

  According to the present invention, the light receiving region for generating the radial error signal is formed in a shape inclined with respect to the radial direction of the optical recording medium, and the areas of the light receiving unit regions on both the left and right sides are made substantially the same, whereby Regardless of this, even if the shape of the light receiving region is set so that the return light is contained within the light receiving region, the area of the light receiving region can be minimized and the band of the light receiving element can be increased. In addition, since there is no difference between the areas of the left and right light receiving portions, it is possible to suppress the occurrence of offset due to the incidence of stray light from the adjacent layers.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the same components as those shown in FIGS. 14 and 15 are denoted by the same reference numerals.

  (Basic Configuration) FIGS. 1, 2 and 3 are basic configuration diagrams of the pickup apparatus of the present invention. In FIG. 1, an optical disk 5 is proposed as a digital versatile disk (DVD) having a two-layer structure in which data layers are stacked with a sufficiently thin interlayer distance, for example, a distance of about 40 to 70 μm, with respect to the thickness of the substrate. It is. Light emitted from the semiconductor laser 1 as a light source is diffracted by the hologram element 2, and the 0th-order diffracted light thereof enters the objective lens 4 through the collimator lens 3 and is condensed on the optical disk 5. Return light from the optical disk 5 is guided to the hologram element 2 through the objective lens 4 and the collimating lens 3.

  As shown in FIG. 2, the hologram element 2 includes a dividing line 2g extending in the y direction corresponding to the radial direction of the optical disc 5, and an x direction orthogonal to the radial direction of the optical disc 5 from the center of the dividing line 2g, that is, the optical disc 5 Are divided into three divided areas 2a, 2b, 2c by dividing lines 2h extending in a direction corresponding to the track direction, and separate gratings are formed corresponding to the divided areas 2a, 2b, 2c, respectively. Yes.

  As shown in FIG. 3, the light receiving element 7 has a region divided into six rectangular light receiving regions 7a, 7b, 7c, 7d, 7e, and 7f arranged in the x direction corresponding to the track direction of the optical disk 5. Have. The central light receiving areas 7 a and 7 b are main light receiving areas for focusing, and are divided by a dividing line 7 x extending in the y direction corresponding to the radial direction of the optical disc 5. 7e and 7f on both sides thereof are auxiliary light receiving areas for focusing, and are arranged at positions symmetrical with respect to the dividing line 7x. The widths W1 and W2 in the x direction of the main light receiving areas 7a and 7b and the auxiliary light receiving areas 7e and 7f are designed to satisfy W1> W2. On the other hand, the light receiving areas 7c and 7d on both sides are radial error detecting light receiving areas, and are provided at a predetermined interval in the x direction with respect to 7e and 7f, and each light receiving element 7a, 7b, 7c, 7d, 7e. , 7f extend in the y direction corresponding to the radial direction.

  Next, the state of return light on the light receiving element will be described. FIG. 4 is an explanatory diagram for explaining the state.

  In the focused state, that is, when the light beam is in a just-focus state on the desired recording / reproducing surface of the optical disc 5, the return light diffracted by the divided region 2a of the hologram element 2 forms a beam P1 on the dividing line 7x. The return light diffracted in the divided regions 2b and 2c forms beams P2 and P3 on the light receiving regions 7d and 7c, respectively. This is because the return light diffracted in the divided region 2a is adjusted to be formed on the dividing line 7x during assembly. The beams P1, P2, and P3 are collected at a position slightly shifted from the center position in the y direction of each light receiving region in order to absorb the positional tolerance of the light receiving element and the wavelength shift of the light by adjusting the position of the hologram element 2. In some cases. In such an in-focus state, the output signals of the main light receiving areas 7a and 7b and the auxiliary light receiving areas 7e and 7f are zero.

  In the case of defocusing, the output signals in the main light receiving areas 7a and 7b and the auxiliary light receiving areas 7e and 7f do not become zero. As shown in FIG. 4 (b) when the optical disk 5 is moved away from the beam P1, the beam P1 expands to one of the light receiving regions 7a or 7b as shown in FIG. 4 (d) when approached. At this time, if the displacement of the objective lens 4 in the focus direction is within the dynamic range Dy of the focus error signal FES, the focus error signal FES (= Sa) is based on the output signals Sa and Sb of the light receiving areas 7a and 7b. -Sb) is generated.

  On the other hand, when the objective lens 4 exceeds the dynamic range Dy and is largely defocused, the beam P1 protrudes from the main light receiving region 7a or 7b as shown in FIGS. It extends to the provided auxiliary light receiving region 7e or 7f. In this case, a focus error signal FES (= (Sa + Sf) − (Sb + Se)) is generated based on the outputs Sa, Sb, Se, and Sf of the light receiving areas 7a and 7b and the auxiliary light receiving areas 7e and 7f.

  Hereinafter, the state of the focus error signal FES in such a basic configuration will be described in detail. First, as a comparative example, the width W1 of the main light receiving regions 7a and 7b is the same as the width W2 of the auxiliary light receiving regions 7e and 7f ( The main light receiving regions 7a and 7b have the same area as the auxiliary light receiving regions 7e and 7f), and this will be described. In FIG. 5A, the solid line indicates the FES curve (F) in this comparative example, and the dotted line indicates the FES curve (F ′) when the auxiliary light receiving regions 7e and 7f do not exist. Until the light beam spot protrudes from the main light receiving region 7a or 7b, that is, within the dynamic range Dy, the FES curve F is the same as F ′, but the light beam spot protrudes from the main light receiving region 7a or 7b and further the auxiliary light receiving region 7e. Alternatively, when the light is incident on 7f, Sf or Se increases, FES = (Sa + Sf) − (Sb + Se) rapidly decreases and converges to zero. That is, when the optical disk 5 moves away from the in-focus position beyond the dynamic range Dy, light reception starts in the auxiliary light receiving area 7f (output Sf) in addition to the main light receiving area 7b (output Sb). In addition to (output Sa), light reception starts in the auxiliary light receiving area 7e (output Se), and in a defocus state exceeding the dynamic range Dy, the difference between (Sa + Sf) and (Sb + Se) is caused by light reception in the auxiliary light receiving areas 7f and 7e. It changes rapidly in the direction of decreasing. Therefore, the focus error signal FES obtained by the calculation of (Sa + Sf) − (Sb + Se) approaches 0 rapidly immediately after exceeding the dynamic range Dy, as indicated by the solid line F in FIG. By changing the shape of the light receiving areas 7e and 7f and the distance between the light receiving areas 7a and 7e or the distances 7b and 7f, the method of reducing FES in the area beyond the dynamic range Dy changes. The FES curve can be brought close to 0 rapidly.

  When the pickup device of this comparative example is applied to the recording / reproduction of an optical disc having a plurality of recording / reproducing layers (two layers) such as a DVD, as shown in FIG. It can be seen that a good FES curve without any is obtained.

  However, in the pickup device of this comparative example, when the hologram element 2 is displaced in the x direction with respect to the optical axis determined by the semiconductor laser 1 and the collimator lens 3 during assembly, the FES curve is as shown in FIG. It will be something. Normally, errors during assembly and laser wavelength deviations are adjusted by adjusting the position of the hologram element 2 and adjusting the rotation with respect to the optical axis so that the focus offset at the time of focusing becomes zero. ), No focus offset occurs at the in-focus position. However, a deviation between the optical axis and the dividing line 2g of the hologram element 2 occurs, and a large peak Pk is generated on the far side (right side in the drawing) as shown in FIG. 5B. When the optical pickup device of the comparative example in which such an assembly error has occurred is applied to recording / reproduction of an optical disc having a plurality of recording / reproduction layers, the FES generates a large focus offset Δ as shown in FIG. Therefore, it becomes difficult to obtain a correct in-focus state.

  The cause of the occurrence of the focus offset Δ in the above comparative example will be described below. 7 and 8 are diagrams for explaining the shape of the return light to each of the four elements, 7a, 7b, 7e, and 7f in the light receiving region and the output signals Sa, Sb, Se, and Sf. These are cases where the dividing line 2g is shifted in the + x direction, and the return light in the defocused state protrudes from the centers of the light receiving elements 7a and 7b. In particular, when the optical disk 5 is shifted to the far side as shown in FIG. 7A, it protrudes larger than when the optical disk 5 is shifted to the near side as shown in FIG. 7B. That is, for example, when there is no assembly error in the defocused state on the far side, the return light is not incident on the light receiving element 7a, but the return light is incident on the light receiving element 7a as it is defocused due to the assembly error. For this reason, although it corrected by Sf so that Sb-Sf may become zero, since the signal part of Sa is added to this, it will be overcorrected and it does not become zero as an FES signal.

  Considering the actual output signal, the focus error signal FES is obtained by the calculation of (Sa + Sf) −Sb + Se), which is modified to (Sa−Se) − (Sb−Sf). First, FIG. 8A shows output signals of Sb and Sf. (Sb−Sf) on the far side (right side in the figure) is almost zero, but on the near side (left side in the figure). Although it converges slowly to zero, it has some numerical values. On the other hand, the figure below shows the output signals of Sa and Se. (Sa-Se) on the near side is almost zero, but on the far side, it has a large peak in the defocused part of about 10 and several μm. .

Therefore, when the main light receiving regions 7a and 7b and the auxiliary light receiving regions 7e and 7f have the same area as in the comparative example, the FES represented by (Sa-Se)-(Sb-Sf) has a large peak on the far side. It has a slight numerical value on the near side. From the above, to prevent overcorrection,
(1) The amount of correction at the auxiliary light receiving unit is reduced.
(2) When an error occurs, the amount of return light protruding from the center of the main light receiving unit is reduced.
The countermeasure can be considered.

  In the basic configuration, since the areas of the auxiliary light receiving regions 7e and 7f are smaller than the main light receiving regions 7a and 7b as described above, the overcorrection can be prevented and a good FES curve can be obtained. .

  FIG. 9 is a diagram showing the FES curve when the widths of the auxiliary light receiving portions 7e and 7f are changed. The left side in this figure is the FES curve when an appropriate assembly error occurs, and the right side is the FES curve when assembled as ideal. In addition, the widths of the auxiliary light receiving portions 7e and 7f are reduced in order from the top. Here, the width W1 of the main light receiving regions 7a and 7b is 25 μm.

  From FIG. 9, when there is an assembly error, the far side peak becomes smaller as the width of the auxiliary light receiving portion becomes smaller. On the other hand, when assembled in an ideal manner, it is understood that a width of about 20 μm (80% of the width of the main light receiving region) is optimal. When the distance is smaller than 20 μm, the FES curve falls slowly in the defocus area, and a large peak does not occur. However, when the layer interval is small, the focus offset is slightly increased. Further, when it becomes smaller and becomes 7 μm, the offset in the ideal state becomes considerably large, and particularly when it becomes 25% or less of the width of the main light receiving region, the offset becomes a problem.

  In an actual optical pickup device, there is always an assembly error, so it is necessary to consider the range of the error and determine the optimal optimum width of the auxiliary light receiving section, even when the error is small (no error). Yes, it is desirable to satisfy 0.25W1 ≦ W2 ≦ 0.8W1 (W1: width of the main light receiving region, W2: width of the auxiliary light receiving region).

  FIG. 10 shows an FES curve when the width W2 of the auxiliary light receiving region is about half of the main light receiving region W1 (W2 = 2 × W1). FIG. 10A shows an ideal state, and FIG. 10B shows an assembly error. (Including mounting on the pickup). In both cases, the generation amount of the focus offset in the region where the focus is greatly defocused is suppressed as much as possible.

In the above example, the problem of overcorrection is solved by making the width of the auxiliary light receiving region smaller than the width of the main light receiving region. However, the optical pickup device of the present invention is not limited to this. For example,
(1) The gain of the output signal from the auxiliary light receiving area is adjusted with a variable resistor or the like.
(2) The FES calculation is performed by the following equation, for example.
FES = (Sa−K × Se) − (Sb−K × Sf), K: Compensation coefficient (3) Decrease the sensitivity of the auxiliary light receiving area itself (change the diffusion density and depth during PD formation).
(4) A shielding band such as a slit is provided in the auxiliary light receiving area to reduce the effective light receiving area.
(5) Shorten the length of the auxiliary light receiving area (because the light beam incident on the auxiliary light receiving area is quite large, even if the light receiving position of the light beam is shifted in the length direction, light can be received reliably)
Thus, it may correspond to a change in the return light shape due to an assembly error or the like.

  (Reference Example) In the optical pickup device of the reference example, (2) the amount of return light protruding from the center of the main light receiving region is reduced when an error occurs in the above basic configuration. FIG. 11 is a cross-sectional view schematically showing the optical pickup device. Here, only the semiconductor laser 1, the light receiving element 7, the hologram element 2, and the collimator lens 3 are described.

  The diffraction angle of the hologram element 2 is designed so that the first-order diffracted light of the reflected light from the optical disc is incident on the light-receiving element 7, but the first-order diffracted light of the forward light beam from the laser 1 is generated similarly. It goes to the collimator lens 3 as shown by the dotted line in the figure.

  In the optical pickup device having such an optical system, the shape change of the return light to the light receiving element 7 due to the above-described assembly error or the like becomes more severe as the diffraction angle θ1 by the hologram element 2 becomes larger. Therefore, in order to reduce the amount of the return light protruding from the center of the main light receiving region, the diffraction angle θ1 by the hologram element 2 may be reduced.

  However, if it is too small, the above-described first-order diffracted light enters the collimator lens 3 and undesirably generates light on the disk. Therefore, if the diffraction angle is reduced to such an extent that the first-order diffracted light in the forward path does not enter the optical element at the next stage of the hologram element 2 such as a collimator lens, a good pickup satisfying both can be configured.

  This will be specifically described below. In FIG. 11, r1 represents the radius of the hologram element 2, r2 represents the radius of the collimator lens 3, θ1 represents the diffraction angle of the return light by the hologram element 2, and θ2 connects the light receiving element 7 and the hologram element 2. The angle between the line segment hologram element 2 and the vertical direction is shown. Further, L is the distance between the light receiving element 7 and the collimator lens 2 (distance in the direction perpendicular to the collimator lens 2), and l is the distance between the light receiving element 7 and the hologram element 2 (in the direction perpendicular to the hologram element). Distance). D indicates a distance between the light receiving element 7 and the semiconductor laser 1 (a distance in a direction parallel to the hologram element 2).

  At this time, tan θ1 = D / l tan θ2 = (D−r1) / l, and thus tan θ1 = (D−r1) / l + r1 / l = tan θ2 + r1 / l.

  Here, the condition for preventing the first-order diffracted light in the forward path from entering the collimator lens 3 is L × tan θ2 ≧ D + r2, and tan θ2 ≧ (D + r2) / L, and therefore tan θ1 ≧ (D + r2) / L + r1 / l. Therefore, if the diffraction angle θ1 is set so as to satisfy this expression, the forward primary light does not enter the collimator lens 3.

  Here, as described above, the diffraction angle θ1 should be as small as possible, so it is desirable that tan θ1 = (D + r2) / L + r1 / l. However, since there are actually assembly errors and the like, the diffraction angle θ1 should be (D + r2 + Δ) / L + r1 / l ≧ tan θ1 ≧ (D + r2) / L + r1 / l, where Δ is the assumed assembly error. Is more desirable.

  FIG. 12 shows the difference in the shape of the return light to the light receiving element when the diffraction angle of the hologram element 2 differs by about twice. (A) has a diffraction angle of about 15 degrees, (b) has a diffraction angle of about 30 degrees, and the diffraction angle is smaller (a), the shift amount from the center of the main light receiving region is smaller, that is, It can be seen that the focus offset amount can be suppressed and a good FES curve can be obtained.

  (Embodiment) FIG. 13 is a schematic view of the essential portion showing the configuration of an optical pickup device according to an embodiment of the present invention. The optical pickup apparatus according to the present embodiment is different from the optical pickup apparatus having the basic configuration shown in FIG. 1 in the shapes of the radial error generating light receiving regions 7c and 7d. Therefore, the same components as those in the basic configuration are denoted by the same reference numerals and description thereof is omitted.

  FIGS. 13A and 13B show the shape of the return light when the return light is most misaligned in the + Y and −Y directions on the light receiving section due to errors such as assembly of the optical system. Further, these drawings show the state of the return light when a certain defocus exists.

  In this state, when returning light is accommodated in the radial error signal generating light receiving areas 7c and 7d regardless of errors, the light receiving areas 7c and 7d have a rectangular shape having sides parallel to the dividing line 7g. Then, the shape shown by the dotted line in the figure is obtained. In the case of such a light receiving region shape, the areas of the light receiving regions 7c and 7d are much larger than the areas of the light receiving regions 7a, 7b, 7e and 7f for generating the focus error signal, and the frequency characteristics are deteriorated. Further, the light receiving area between the light receiving regions arranged on the left and right sides is different, and a difference occurs in the frequency characteristics of the left and right light receiving elements. Furthermore, when reproducing a plurality of recording / reproducing discs, stray light from an adjacent layer is incident, but a radial offset occurs because the left and right areas are different.

  In order to solve the above problem, as indicated by the solid line in FIG. 13, the area of the light receiving portion must be made as small as possible and the areas of the light receiving regions 7c and 7d on both the left and right sides should be substantially the same. . That is, it is necessary to make the shape inclined with respect to the dividing line 7g according to the moving direction of the beam. By setting in this way, the area of the light receiving region is about half or less than that of the dotted line, and it is possible to suppress the difference from the area of the light receiving part for generating the focus error signal. It will not be an obstacle. Also, since the left and right light receiving area can be made the same, there is no difference in the frequency characteristics of the light receiving elements, and even when stray light from adjacent layers is incident when reproducing multiple recording / reproducing discs, Are the same, no radial offset occurs.

  As described above, in the optical pickup device of the present invention, since the auxiliary signal from the auxiliary light receiving area for correcting the focus error signal is adjusted, the offset in the FES even when the shape of the return light changes due to an assembly error or the like. Can be suppressed.

  In addition, by setting the area of the auxiliary light receiving area to be smaller than the area of the main light receiving area, an error due to assembly or the like occurs, and even if the shape change of the return light to the light receiving element when the focusing operation is performed is large. It is possible to suppress the correction of the focus error signal in the defocused state from being overcorrected or undercorrected.

  When the area of the auxiliary light receiving area is 80% or less and 25% or more with respect to the area of the main light receiving area in the photodetector, even if errors occur due to assembly, etc., or almost no errors occur However, when the focus operation is performed, the shape change of the return light to the light receiving element is different, so that the correction of the focus error signal in the largely defocused state is overcorrected or conversely undercorrected. It can be suppressed more.

  The diffraction angle of the hologram element is set so small that the outgoing first-order diffracted light does not enter the next lens system (for example, a collimator lens or an objective lens). The shape change of the return light to the light receiving element when the focus operation is performed is different, but the difference can be reduced. As a result, it is possible to suppress the correction of the focus error signal from being overcorrected or conversely insufficiently corrected, so that a good FES curve is obtained when recording / reproducing an optical disc having a plurality of recording / reproducing layers. It becomes possible.

  Furthermore, a light receiving area for generating a radial error signal is formed along the moving direction of the return light due to an error such as assembly, and the areas of the light receiving area on both the left and right sides are substantially the same, so that the return light is not affected by the above error. Even if the shape of the light receiving region is set such that the light receiving region falls within the light receiving region, the area of the light receiving region can be minimized and the bandwidth of the light receiving element can be increased. In addition, since there is no difference between the areas of the left and right light receiving portions, it is possible to suppress the occurrence of offset due to the incidence of stray light from the adjacent layers.

  The optical pickup device of the present invention emits a light beam from a light source, condenses the light beam on the optical recording medium, and detects the return light from the optical recording medium. A main light receiving unit that has at least two main light receiving areas on which return light according to a focus shift is incident, and generates a main signal according to the amount of light incident on each main light receiving area; and protrudes from at least two main light receiving areas The auxiliary light receiving area that receives the return light, generates auxiliary signals according to the amount of light incident on the auxiliary light receiving area, and generates the focus error signal by correcting the main signal using the auxiliary signal. The auxiliary signal may be adjusted so as to cope with a change in the shape of the return light based on the arrangement error of the optical system.

  According to the above configuration, at least two main light receiving areas that generate a main part of the focus error signal and an auxiliary light receiving area that detects light that protrudes from the main light receiving area when the defocus state is achieved. The focus error signal is corrected by the auxiliary signal from the auxiliary light receiving area. In addition, the auxiliary signal is adjusted so as to cope with a case where the return light shape changes due to an arrangement error such as an assembly error generated in the optical system. Therefore, the focus error signal offset can be suppressed.

  The optical pickup device of the present invention may be configured such that, in the optical pickup device configured as described above, the area of the auxiliary light receiving region is set smaller than the area of the main light receiving region.

  According to the above configuration, since the area of the auxiliary light receiving region is set smaller than that of the main light receiving region, the auxiliary signal can be adjusted with a simple configuration. In addition, it does not become an obstacle to increase the bandwidth of the light receiving element.

  The optical pickup device of the present invention may be configured such that, in the optical pickup device having the above-described configuration, the area of the auxiliary light receiving region is 25% or more and 80% or less of the area of the main light receiving region.

  According to the above configuration, by optimizing the area of the auxiliary light receiving region, the focus error signal in the state of being greatly defocused both in the case where an arrangement error due to assembly or the like occurs and in the case where almost no error occurs. It is possible to further suppress the correction from being overcorrected or conversely being insufficiently corrected.

  The optical pickup device of the present invention emits a light beam from a light source, condenses the light beam on the optical recording medium through another optical system after passing through the hologram element, and from the optical recording medium. In the optical pickup device that diffracts and detects the return light of the light beam by the hologram element, the optical pickup device has at least two main light receiving areas on which the return light according to the defocus of the light beam is incident. A main light receiving means for generating a corresponding main signal and an auxiliary light receiving area for receiving return light that protrudes from at least two main light receiving areas, and generating an auxiliary signal according to the amount of light incident on the auxiliary light receiving area And an error signal generating means for generating a focus error signal by correcting the main signal using the auxiliary signal, and the first-order diffraction angle by the hologram element is a light source. 1 by the hologram element of the optical beam may be diffracted light is the limit angle substantially the same angle does not enter the other optical system configuration.

  The optical pickup device having the above-described configuration is assembled because the diffraction angle of the hologram element is made small so that the first-order diffracted light in the forward path does not enter the next lens system (for example, a collimator lens or an objective lens). When an error due to the above occurs, the shape change of the return light to the light receiving element when the focusing operation is performed is different, but the difference can be reduced. Since it is possible to suppress the focus error signal from being overcorrected or conversely insufficiently corrected, it is possible to obtain a good FES curve when recording / reproducing an optical disc having a plurality of recording / reproducing layers. It becomes.

  Incidentally, the fact that the first-order diffraction angle by the hologram element is substantially the same angle as the limit angle includes that in which an assembly error is added to the limit angle in consideration of an assembly error or the like.

  According to the present invention, the bandwidth of the light receiving element can be increased. In addition, since there is no difference between the areas of the left and right light receiving portions, it is possible to suppress the occurrence of offset due to the incidence of stray light from the adjacent layers.

It is a schematic block diagram of the optical pick-up of this invention. It is a schematic diagram which shows the structure of the hologram element in FIG. It is the schematic which shows the structure of the light receiving element in FIG. It is explanatory drawing which shows the mode of the return light in the state which the optical disk approached and the state which moved away. It is explanatory drawing of the FES curve in the auxiliary light-receiving area | region shape of a comparative example. It is explanatory drawing of the FES curve in the case of recording / reproducing a 2 layer disk with the optical pick-up apparatus of the auxiliary light-receiving area shape of a comparative example. It is explanatory drawing which shows the shape of the return light at the time of defocus in the auxiliary light-receiving area | region shape of a comparative example. It is explanatory drawing which shows the output signal of each light reception area | region in a comparative example. It is a figure explaining the FES curve at the time of changing the width | variety of an auxiliary light reception area | region. It is the schematic of the FES curve in the case of the area of a main light reception area | region = 2x the area of an auxiliary light reception area | region. It is a block diagram of the principal part of the optical pick-up apparatus of a reference example. It is the schematic which shows the shape of the return light from a disc in case diffraction angle (theta) differs. It is the schematic showing the shape of each light-receiving area | region in embodiment of this invention, and the shape of the return light from a disc. It is the schematic which shows the structure of the pick-up apparatus which the present applicant previously proposed. It is explanatory drawing which shows the structure of the light receiving element in FIG.

Explanation of symbols

2 Hologram element 7 Light receiving elements 7a, 7b Main light receiving areas 7e, 7f Auxiliary light receiving areas 7c, 7d Light receiving area 7g for generating radial error signal Dividing line

Claims (1)

In an optical pickup device that emits a light beam from a light source, condenses the light beam on an optical recording medium, and detects return light from the optical recording medium.
A focus control unit that has at least two main light receiving regions into which return light according to a focus shift of the light beam is incident, and generates a focus error main signal according to the amount of light incident on each main light receiving region;
The at least two main light receiving regions are arranged so as to be sandwiched from both sides, and have two radial error detection light receiving regions on which return light from the optical recording medium is incident, and the incident light quantity to the radial error detection light receiving regions Radial control means for detecting a radial error signal from,
A light beam emitted from the light source is condensed on the optical recording medium using a collimating lens and an objective lens, and return light from the optical recording medium is collected using the objective lens, the collimating lens, and a hologram element. An optical system that divides the light into two divided light beams and makes the light beams incident on each of the two radial error detection light-receiving regions.
The hologram element is divided into two in a direction orthogonal to the radial direction of the optical recording medium, and one of the regions divided in the direction orthogonal to the radial direction is divided into two in the radial direction. Return light from the optical recording medium incident on each of the regions divided in the radial direction is the two divided lights,
The light source, the collimating lens, the objective lens, and the hologram element are arranged along the optical axis direction of the light beam emitted from the light source so as to constitute the optical system ,
Before Symbol light source, the collimating lens, the when the objective lens and the hologram element is disposed so as to constitute the optical system, the optical axis direction of the distance between the hologram element and the two radial error-detecting light-receiving region When an arrangement error that is an error occurs, the incident angle at the time when the two divided lights enter the respective radial error detection light receiving regions due to the arrangement error and the respective radial error detection light receptions. When the optical path length until the light enters the region varies, the incident position of each of the divided lights in each of the two radial error detection light-receiving regions moves in each of the radial error detection light-receiving regions, and direction incident position of each divided light is moved due to the placement error, Ri Monodea shifted by different angles with respect to the radial direction of the optical recording medium
Each of the two radial error detection light-receiving regions is inclined with respect to the radial direction of the optical recording medium so that the incident position of the divided light incident thereon is along the direction of movement due to the placement error. Formed into a shape,
2. The optical pickup device according to claim 1, wherein the two radial error detection light-receiving regions have different shapes, and the two radial error detection light-receiving regions have substantially the same area.

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